Mobile telephone service provides a means for telephone conversations to be originated from or terminated at, a moving vehicle or portable unit. Typically, frequency modulation (FM) radio channels are used as links between mobile units comprising wireless terminals and a mobile telephone switching office (MTSO) via base stations that serve geographically localized mobile subscribers. Furthermore, cellular techniques are presently utilized in order to enable high volume traffic to operate over a limited number of available radio channels allocated by the Federal Communications Commission (FCC). Typically, in cellular systems, by dividing large geographical areas, called cells, into smaller geographical areas or microcells, the same radio channels in different microcells may be reused.
While this new cellular architecture greatly increases the traffic volume which may be handled, sophisticated routing and switching equipment is required to maintain the integrity of each call as a subscriber moves from one cell to another. In particular, as an active subscriber moves from cell to cell, the switching system assigns a new radio frequency channel and, moreover, assigns appropriate communications resources to route signals from and to the new cell and the called party. Unfortunately, as the number of active subscribers increases dramatically and the size of the cell is further decreased in order to handle the traffic volume, a greater demand is placed on the switching architecture because of the increased frequency with which active subscribers cross cell boundaries. It is anticipated that within the next few years, the required switching capacity will become prohibitively large for existing mobile cellular switches and the associated mobile network architectures.
Various proposals have been suggested to alleviate the anticipated demand for mobile radio service. While larger cellular switches may be able to handle the increase traffic volume, they are relatively expensive and may not be readily available for short terms needs. More importantly, circuit switch architectures and network architectures of present cellular systems generally do not afford extended coverage on demand. In particular, D. J. Goodman has suggested a switching architecture which greatly relieve the switching burden due to increasing boundary crossing as cellular cells become smaller. See U.S. Pat. No. 4,916,691, which is commonly assigned and incorporated herein by reference. In particular, Goodman teaches dividing packet of information into two segments; those which change with cells as a subscriber crosses a cell boundary and those that do not change as the active subscriber moves from cell to cell. Routing procedures associated with information which do not change between cell boundaries may be stored in the memory of the switch only once, at the beginning of the call. However, routing procedures associated with the information that do change may be derived from the header of its packet received by the switch. As such, an exemplary switching architecture would comprise two separate units, one of which establishes the initial route and the other which is used to vary only that portion of the header which changes as a subscriber crosses a cell boundary. While this cellular architecture and the associated infrastructure permits rapid growth by distributing many of the switching and control functions to additional modulator units which may be added as warranted by the traffic volume, it is highly desirable to mitigate the need for additional modular units, reduce the complexity of switching operations associated therewith and further reduce the switching burden on switches.